1. Field of the Invention
The present invention relates to a process for producing a styrenic polymer and a catalyst for use therein. More particularly, it pertains to a process for efficiently producing a styrenic polymer having a high degree of syndiotactic configuration in the stereochemical structure of the polymer main chain and to a catalyst to be used for the process.
2. Description of the Related Arts
It has recently been disclosed by the research group of the present inventors that a styrenic polymer having a syndiotactic configuration is obtained by polymerizing a styrenic monomer by the use of a catalyst comprising as primary ingredients a transition-metal compound, especially a titanium compound and an alkylaluminoxane (Refer to Japanese Patent Application Laid-Open Nos. 187708/1987, 179906/1988, 241009/1988, etc.).
Methylaluminoxane, particularly suitable as an alkylaluminoxane is obtained usually by the reaction between trimethylaluminum and water. However, the above-mentioned reaction involves the problem that the reaction is difficult to put into practical production because of its violent reaction, and further suffers the disadvantage that in addition to requiring expensive trimethylaluminum as the starting material, an excessively large amount of methylaluminoxane is required as a component of the catalyst as compared with the quantity of a transition metal, thus causing an extremely expensive catalyst.
There has recently been reported that a polymerization catalyst not containing aluminoxane is capable of polymerizing .alpha.-olefin (principally, ethylene) by R. Taube (J. Organomet. Chem. C9-C11, 347 (1988)), H. Turner (J. Am. Chem. Soc. 111,2728 (1989)), R. F. Jordan (Organomet. 8,2892 (1989)), etc. Nevertheless, investigation has not yet been made on a polymerization catalyst not containing aluminoxane for the polymerization of styrenic monomer, leaving the problem that styrenic monomer, different from .alpha.-olefin, is likely to be polymerized into an atactic polymer in the presence of a cationic species.